Lightning or surge arresters are typically connected to power lines to carry electrical surge currents to ground, and thus, prevent damage to the lines and the equipment connected thereto. Arresters offer high resistance to normal voltage across power lines, yet offer very low resistance to surge currents produced by sudden high voltage conditions, caused, for example, by lightning strikes. After the surge, the voltage drops and the arrester should normally return to a high resistance condition. However, upon arrester malfunction or failure, the high resistance condition is not resumed by the arrester, and the arrester continues to provide an electrical path from the power line to the ground. The line will ultimately lockout due to the short circuit condition or breakdown of the distribution transformers. Additionally, the arrester will have to be replaced.
To avoid line lockout, isolators or disconnectors are commonly used in combination with the arresters to separate a malfunctioning arrester from the circuit and provide a visual indication of arrester failure. Isolators or disconnectors have an explosive charge to destroy the circuit path and physically separate the electrical terminals of the isolator. Known isolators are disclosed in U.S. Pat. Nos. 5,057,810 and 5,113,167 to Raudabaugh.
Conventionally, as disclosed in the two Raudabaugh patents, the arrester is located between the power line and the disconnector or isolator. Specifically, the lightning or surge arrester is connected directly to the power line while the isolator or disconnector is located between the arrester and the ground, such that the power line, arrester, isolator and ground are connected in series and in that sequence. Other examples of this conventional arrangement of the surge arrester and isolator are disclosed in U.S. Pat. No. 2,305,435 to McMorris and U.S. Pat. No. 4,710,847 to Kortschinski.
U.S. Pat. No. 2,464,565 to Evans discloses a lightning arrester assembly in which the lightning arrester is coupled to a power line through a lead line, a disconnecting device and a cut-out device. The cut-out device is connected both to a transformer and a power line. The disconnecting device is mechanically actuated upon shattering of the arrester top. The shattering of the arrester top and its movement from the separated bottom portion of the arrester top causes a mechanical disengagement and separation of the two connected terminals of the disconnecting device. In this manner, the arrester assembly according to the Evans patent requires fracturing and separation of the upper and lower portions of the arrester to effect separation of the disconnecting device terminals. If the arrester fails electrically, without exploding and breaking apart, the Evans device does not separate the disconnecting device.